This invention relates to sensing strain in hydrocarbon wells. The invention is particularly concerned with sensing strain experienced by the casing of a hydrocarbon well.
During the extraction of hydrocarbons, the medium surrounding the well, for example earth and rocks, can experience compaction. This, in turn, applies strain to the casing of the hydrocarbon well. It is desirable to be able to monitor the strain being experienced by the casing.
Previous sensing arrangements have incorporated a number of strain gauges fitted to the casing. However, the casing is typically several kilometers long, necessitating a large number of strain gauges and a complex arrangement to extract strain data from each sensor.
The invention provides apparatus for sensing strain applied to a region of a hydrocarbon well, comprising an optical fiber in communication with the region, the optical fiber being responsive to strain applied to the region and to a light signal transmitted through it, in order to produce a sensing light signal incorporating scattered light, wherein a characteristic of the scattered light is indicative of the strain being applied to the region.
Preferably, the characteristic of the scattered light being monitored is so-called Brillouin scattering.
The provision of a single optical fiber in order to sense strain being applied along a relatively large area simplifies the sensing of strain.
The invention will now be described, by way of example, with reference to the accompanying drawings.